-pointer to the RTTI type descriptor for the object to catch. The third argument
-is a pointer to a function implementing the catch. This function returns the
-address of the basic block where execution should resume after handling the
-exception.
+pointer to the RTTI type descriptor for the object to catch. The second
+argument is an index into the argument list of the ``llvm.frameescape`` call in
+the main function. The exception object will be copied into the provided stack
+object. If the exception object is not required, this argument should be -1.
+The third argument is a pointer to a function implementing the catch. This
+function returns the address of the basic block where execution should resume
+after handling the exception.